[Elution kinetics and antimicrobial effects of gentamicin- and clindamycin-loaded bone cements in vitro]. / In-vitro-Untersuchungen zu Elutionskinetiken und antimikrobiellen Wirkungen von Gentamicin- und Clindamycin-haltigen Knochenzementen.

AIMS: In arthroplasty and particulary in revision surgery antibiotic-loaded bone cements are applied. The purpose of the current study was to analyse the kinetics of antibiotic release and antimicrobial effects of the gentamicin- and clindamycin-loaded bone cement Versabond. MATERIALS AND METHODS: Test cylinders of bone cements, containing gentamicin and clindamycin in different concentrations, were investigated in vitro with regards to the kinetics of antibiotic release by applying static and continuous elution methods. Antimicrobial effects of antibiotic-loaded bone cement were tested in an infection model with different strains of Staphylococcus aureus and Staphylococcus epidermidis and live/dead dye plus fluorescence microscopy. For the surface analysis of antibiotic-loaded test cylinders contaminated with Staphylococcus epidermidis, scanning electron microscopy was used. RESULTS: The measurement of static and continuous elution revealed initially higher rates of gentamicin release in comparison with clindamycin. The gentamicin amount decreased within 24 h, whereas clindamycin-loaded test cylinders showed a prolonged release. After 24 h exclusive avital bacteria on antibiotic-loaded cement cylinders were seen, after 72 h on gentamicin-loaded cement bacterial growth was again detected. Application of antibiotics in bone cement revealed an inhomogeneous surface of the bone cement cylinder. CONCLUSIONS: On application of clindamycin in bone cement the features of increased antibiotic uptake and antimicrobial effect compared with gentamicin-loaded bone cement are observed.

Plasma transglutaminase factor XIII induces microvessel ingrowth into biodegradable hydroxyapatite implants in rats.

Coagulation factor XIII is a member of the transglutaminase-family. Transgluaminases cross-link either fibrin monomers in blood coagulation or extracellular proteins in extracellular matrix formation. In early stages of bone healing migration and proliferation of endothelial cells lead to formation of new vessels. The aim of this study was to investigate the angiogenetic activity of plasma factor XIII in bone defects filled with nanoparticulate hydroxyapatite paste. A critical size defect was created in the tibial head of rats which was not filled in group I. In group II the defect was filled with hydroxyapatite paste, and in group III with hydroxyapatite paste enriched with factor XIII. Ten days after surgery angiogenesis in the defects was assessed using immunohistochemistry and confocal laser scanning microscopy. Ac16 antibody was used to detect activation of factor XIII into factor XIIIA. In defects without biomaterial (group I) vessel-rich connective tissue and diffuse distribution of capillaries was observed. In defects filled with pure hydroxyapatite (group II) formation of capillaries was limited to the host bone-hydroxyapatite interface. In contrast, addition of plasma factor XIII to hydroxyapatite (group III) stimulated formation of vessels within the biomaterial. The current study reveals that factor XIII can improve angiogenesis in hydroxyapatite.

[Nanoparticulate silver. A new antimicrobial substance for bone cement]. / Nanopartikuläres Silber. Ein neues antimikrobielles Agens für Knochenzement.

BACKGROUND: Multiresistant bacteria have become an important problem in prosthetic joint infections. Their frequent resistance against gentamicin, which is commonly used in antibiotic-loaded bone cements, makes a new prophylaxis necessary. METHODS: PMMA-cement was loaded with 1% nanoparticulate silver and its antibacterial activity tested in vitro against gentamicin-resistant MRSE and MRSA strains as well as being compared to the activity of plain and gentamicin-loaded bone cements. A quantitative elution testing was also done to study the potentially cytotoxic effects of NanoSilver cement. RESULTS: Unloaded and PMMA-cement loaded with 2% gentamicin did not exhibit any antibacterial activity against MRSE and MRSA. At 1%, NanoSilver cement completely inhibited the proliferation of MRSA and MRSE. NanoSilver bone cement did not show any significant differences compared to the non-toxic control group. CONCLUSIONS: If these promising in vitro results can be confirmed in vivo, NanoSilver bone cement may be of considerable value in total joint arthroplasty.

[Vacuum mixing systems for bone cement completion - comparison of different systems]. / Vakuummischsysteme zur Knochenzementfertigstellung - Ein Vergleich unterschiedlicher Systeme.

INTRODUCTION: The use of vacuum mixing systems when mixing bone cement reduces its porosity and hereby significantly improves the features of the material. The currently available mixing systems are compared with regard to handling, mechanical properties and economical aspects. METHODS: In 8 vacuum mixing systems the handling, pump performance, system tightness, the used air volume, the filter efficiency, the remaining amounts in the mixing system and the porosity of the cements are shown in comparison. RESULTS: All vacuum mixing systems reduce the porosity of the cement in comparison to hand mixed cements significantly if used correctly. The individual examinations, though, show enormous differences, which can be of significance to the user in the individual choice of system and, depending on the individual circumstances, can influence the quality of the mixed cement. CONCLUSION: The results enable the user to choose and handle a vacuum mixing system which is optimally suitable for the individual circumstances in respect to the characteristics examined.

Elution characteristics of vancomycin, teicoplanin, gentamicin and clindamycin from calcium sulphate beads.

The in vitro release of vancomycin, teicoplanin, gentamicin and clindamycin from biodegradable calcium sulphate (CaSO(4)) carrier beads is described. All antibiotics showed prolonged release from the carrier beads, which was elevated during the first 24 h, with peak levels exceeding 2500 microg/bead. Doubling the antibiotic load of the beads revealed a more prolonged elution and a two-fold increase in antibiotic release. Local carrier-associated antibiotic treatment with CaSO(4) beads may prove to be effective in the management of chronic bone infections.

[Defect reconstruction using demineralized bone matrix. Experimental studies on piglets]. / Defektaufbau mit demineralisierter Knochenmatrix. Experimentelle Untersuchungen beim Minischwein.

The aim of this study was to evaluate the bone stimulation forced by Demineralized Bone Matrix (DBM)-Chips and-Gel in comparison to the bone-ingrowth into a porous hydroxylapatite ceramic (Endobon) in mini pigs. The following results were obtained: 1. DBM-Chips and DBM-Gel did not stimulate bone healing when filled into cancellous bone defects. The defect did not heal within 12 weeks. 2. Up to 35 days the least amount of new bone formation was observed within porous hydroxylapatite ceramic. Up to 12 weeks complete bone ingrowth in to the ceramic has been seen with close bonding between new formed bone and the ceramic trabeculae. 3. By continuous labelling with fluorochromes the new bone formation could be analysed by fluorescence microscopy and the dynamics could be related to time after implantation.

Influence of sterilization upon a range of properties of experimental bone cements.

Bone cement, used to fix prostheses into the bone, must be sterilized prior to implantation. Two sterilization techniques, gamma and beta radiation, were investigated, examining the influence upon molecular weight, static and dynamic mechanical characteristics and rheological properties. A number of experimental cements were studied prepared from methylmethacrylate (MMA) co-polymers, either single powders or powder blends, mixed with MMA monomer. It was found that with both gamma and beta radiation, there was a decrease in molecular weight of all powders, including a MMA/styrene co-polymer, in relation to the radiation dose. This fall in molecular weight resulted in a drop in tensile strength, Young's modulus and strain to failure of all cements tested. However, the deterioration in mechanical strength was highlighted by the dynamic testing. Fatigue lives of cements after testing in tension-tension, at 2 Hz under load control and irradiated with 25 kGy gamma radiation, displayed significant decreases. This result indicated the utmost importance of conducting such tests upon experimental bone cements prior to in vivo use. The rheological time profiles of curing cements were also found to be influenced by 25 kGy gamma radiation, with a reduction of complex viscosity after sterilization.

The release of gentamicin after total hip replacement using low or high viscosity bone cement. A prospective, randomized study.

Low viscosity bone cement is expected to give improved long term fixation of prosthetic components by increased intrusion into cancellous bone. Fixation is more difficult to achieve after revision for infection because of the inferior quality of the bone. We have compared the amount of gentamicin released from high viscosity and low viscosity bone cements in 41 patients undergoing total hip replacement. The concentration of gentamicin in serum and the wound secretion, and the amount recovered from the urine, was about three times higher for low viscosity cement. A possible explanation for this is an increase in surface area of the cement body because of improved intrusion of cement into bone. The improved mechanical fixation and the high concentration of gentamicin of the bone cement interface favours the use of low viscosity cement, especially in revision for deep infection.

Reaction of the bone structure to methotrexate-Palacos flow y. Experimental investigations in animals.

With the combined osteosynthesis of pathological fractures in association with tumors and/or metastases in mind, E. Merck (Darmstadt, FRG) developed a bone cement containing a cytostatic agent, methotrexate-Palacos flow y (MTX-Pf). The animal-experimental study presented here investigates the tolerability of MTX-Pf in the femurs of rabbits with lateral comparison. In these investigations we used both the concentration of 0.63% MTX, as is currently used in standard clinical surgery, as well as a much higher concentration of 2.5% MTX. The histological sections were investigated using microradiographic methods and provided no indication of any significant differences between the femora with the MTX-Pf implantation and those into which standard Palacos flow y had been implanted.

[Bone cement containing cytostatic drugs: new aspects in the treatment of malignant bone tumors. I. Experimental studies]. / Cytostaticahaltiger Knochenzement: Neue Aspekte in der Behandlung maligner Knochentumoren. I. Experimentelle Untersuchungen.

Radical surgery in malignant bone tumors can either be limited by anatomical structures or seems inadequate in the palliative stabilization of bone metastases. Incomplete removal of the tumor and stabilization by compound osteosynthesis or endoprosthesis contains two problems: 1) the wide spread of malignant cells by manipulation in the tumor bearing area; 2) progressive destruction of bone due to remaining tumor. To overcome these problems we developed methotrexate bone cement (MTX-Palacos) with the aim to obtain high local concentrations of methotrexate in order to destroy remaining tumor cells and avoid systemic side effects. In vitro studies showed that methotrexate is released continuously from this cement without relevant changes of its biomechanical properties. Animal studies with transplanted osteosarcomas and mamma carcinomas in mice showed a considerable decrease of tumor growth when a plug of MTX-Palacos was inserted in the center of the tumor. Histological findings showed that in the surroundings of the plug the tumor was destroyed considerably contrary to normal bone cement which had no effect on the tumor at all. The results are discussed with regard to clinical application of MTX-Palacos.

The intraneoplastic chemotherapy in a rat brain tumour model utilizing methotrexate-polymethylmethacrylate-pellets.

In an experimental glioma model, using ethylnitrosourea induced and subsequently intracerebrally implanted tumours in BD-IX rats, the effectiveness of intratumoural application of methotrexate (MTX) by stereotactic implantation of polymethylmethacrylate (PMMA) pellets containing MTX, has been studied. Tumour volume 10 days after pellet implantation as well as survival rates of treated, untreated and control animals have been the criteria of the effect of treatment. Tumour volume was significantly smaller in treated compared to untreated animals. The survival rate of untreated to treated animals increased 150 and 233% respectively when compared with the control animals. Thus a positive therapeutic effect of MTX-PMMA pellet implantation in the experimental glioma could be proven. Possible consequences for the treatment of human gliomas are shortly discussed.

Pharmacokinetic study of gentamicin-loaded cement in total hip replacements. Comparative effects of varying dosage.

A randomised, double-blind study was performed in two groups of 15 patients undergoing total hip replacements, using antibiotic-loaded acrylic cement containing 0.5 g and 1.0 g gentamicin base respectively per 40 g pack of powdered polymer. Postoperatively, the gentamicin levels in the blood, in the urine and in the wound drainage fluid were measured. In both groups of patients, the serum gentamicin concentrations were low whereas the wound drainage fluid contained highly effective antibacterial concentrations. Serum, urine and wound secretion levels showed approximately two-fold higher concentrations in the group of patients receiving the higher gentamicin load.

Antibiotics and bone cements. Experimental and clinical long-term observations.

Comparing several antibiotics and different bone cements, the mixture of Palacos R (polymethylmethacrylate, PMMA) with gentamicin proved to be the most suitable one as far as a high and sustained release of the antibiotic from the artificial resin is concerned. A continuous leaching of gentamicin was observed for more than 5 years. Gentamicin proved to be stable in Palacos R for the whole period of time. The release of 12 antibiotics from Palacos R was evaluated in vitro. Four other bone cements were included in this study as well, in order to evaluate the leaching of gentamicin from these materials. The combination Gentamicin-Palacos R (GP) showed a 2--3 fold higher and much more prolonged release than did the other mixtures. From this investigation, which also included studies of commercially available antibiotic bone cement mixtures, it is quite obvious that there exist distinct differences in the various bone cements as well as in the various antibiotics as regards their qualification for use in alloarthroplasty. Pharmacokinetic studies in patients after implantation of GP showed low gentamicin concentrations in serum (on average 1.8 microgram/ml) and urine. However, in wound exudate, derived directly from the vicinity of the implanted cement, gentamicin concentrations up to 150 micrograms/ml were observed. Also in tissue samples from the vicinity of the implant, high concentrations were measurable for a long period of time (up to 5 1/2 years).

[Experimental and pharmacokinetic studies with gentamicin PMMA beads (author's transl)]. / Experimentelle und pharmakokinetische Untersuchungen mit Gentamycin-PMMA-Kugeln.

Gentamicin PMMA beads (PMMA = polymethylmethacrylate) represent a new form of local antibiotic therapy for treating chronic bone and soft tissue infections. Gentamicin is released in high concentrations from PMMA. The therapeutic efficacy of the beads was demonstrated in a model of bone infection in dogs. Sufficiently high tissue concentrations of gentamicin were measurable for a period of 4 months. A very good tolerance of the beads was demonstrated in dogs as well as in cell cultures. High gentamicin concentrations exceeding the MBC values of relevant pathogens were measurable in patients at the site of infection. Serum and urine concentrations were low and therefore toxic side effects are excluded.

Bactericidal activity of cefazedone.

Distinct bactericidal activity of (6R,7R)-7-(2-[3,5-dichloro-4-oxo-1(4H)-pyridyl]-acetamido)-3-([(5-methyl-1,3,4-thiadiazol-2-yl)-thio]methyl)-8-oxo-5-thia-1-aza-bicyclo[4,2,0]oct-2-ene-2-carboxylic acid (cefazedone, Refosporen) could be demonstrated in 2 Staphylococcus aureus and 3 Escherichia coli strains. The effect was less in 1 strain of Proteus mirabilis. Whereas the activity in serum and bile was higher than in nutrient broth, the bactericidal activity in urine was less pronounced. The combination of cefazedone and gentamicin proved to be bactericidal in low concentrations.